Electromagnetic coils are useful for generating and measuring magnetic fields in a variety of settings. Such coils can be incorporated into a wide array of devices and systems including, for example, inductors, transformers, electric motors, and larger systems that incorporate such components. As just one example, the electromagnetic coils in an electric motor can enable it to precisely position a semiconductor wafer during photolithography and other semiconductor processing. Alternately, coils and electric motors are used in many other devices including, for example, elevators, electric razors, machine tools, metal cutting machines, inspection machines and disk drives.
An electromagnetic coil is generally formed from a wire wound multiple times around a core or form. The wire usually includes a conductor within an insulative coating or jacket that electrically isolates consecutive windings or “turns” of the conductor. As an electric current is passed through the conductor, the windings generate a magnetic field that can be used to, for example, generate movement within an electric motor. Conversely, when the coil is placed within an external magnetic field, the windings generate an electric current corresponding to the rate of change of the external field.
In addition to desired effects, a coil can generate heat due to the inherent resistance that currents encounter within the coil windings. Excessive heat can damage the coil or components within its surrounding environment and as such, effectively limits the amount of power that can be applied to the coil. Short of irreversible damage, undesired heat can also affect the performance of a coil or the device incorporating the coil. For example, excessive heating of the coils of an electric motor can increase the resistance of the coils, exacerbating the heat problem and reducing the performance of the motor. In addition, heat can cause the thermal expansion of machine components, resulting in inaccuracy of precision mechanical systems.
Systems for mitigating heat generation within a coil include both passive and active cooling systems. For example, heat sinks draw thermal energy away from the coil and often provide an extended surface area for more effective cooling. In other systems, a fluid flowing past the coil removes heat to cool the coil.
Even with these types of aids, however, there remains a need for improved systems for reducing the effect of excess coil heat. Further improvements in heat mitigation can, for example, allow a higher operating power, more compact or more powerful motors, and/or the use of a greater variety of less heat-resistant materials. In addition, there remains a need for improved heat handling within high precision systems, especially as the degree of required precision increases. For example, linear and planar motors used in machines such as, for example, photolithography devices, must be able to precisely position objects (e.g., a stage for a semiconductor substrate or reticle) at ever-decreasing tolerances, despite excess heat generated by the coils of the motors.